1. Field
Disclosed herein is a method whereby the valuable metals contained in a sulphidic concentrate are recovered from a concentrate that contains several valuable metals, using hydrometallurgical treatment. One constituent of the concentrate is copper sulphide, which is leached with an alkali chloride-copper (II) chloride solution. The sulphides of other valuable metals, such as zinc, nickel, cobalt and lead are leached before copper leaching and are each recovered as a separate product before copper recovery.
2. Description of Related Art
U.S. Pat. No. 6,007,600 describes the method developed by Outokumpu Oyj for the hydrometallurgical fabrication of copper from a copper-containing raw material such as copper sulphide concentrate. According to the method, the raw material is leached using countercurrent leaching with a concentrated alkali chloride-copper (II) chloride solution in several stages to form a copper (I) chloride solution. Since there are always both divalent cupric chloride and impurities formed from other metals remaining in solution, reduction of the divalent copper and solution purification is performed on the solution. The pure copper (I) chloride solution is precipitated by means of alkali hydroxide into copper (I) oxide and the oxide is reduced further to elemental copper. The alkali chloride solution formed during copper (I) oxide precipitation is further treated in chlorine-alkali electrolysis, from which the chlorine gas and/or chloride solution obtained is used for raw material leaching, the sodium hydroxide formed in electrolysis is used for oxidule precipitation, and the hydrogen produced for the reduction of copper into elemental copper. The method is called the HydroCopper™ process. U.S. Pat. No. 6,007,600 refers to the recovery method of copper as a whole, but it relates mainly to pure copper sulphide concentrates.
U.S. Pat. No. 5,487,819 describes the method developed by Intec Ltd for the hydrometallurgical fabrication of copper from raw materials such as sulphide concentrate that contain copper and possibly other valuable materials. According to the method the raw material is leached in counter-current leaching with a sodium chloride-copper chloride solution in several stages. If there are other sulphides in the raw material apart from copper sulphide, the method describes that the other sulphides are leached in the first stage of leaching, from which stage the solution is removed for further treatment. Leaching of the undissolved raw material continues, forming a copper (I) chloride solution and precipitate containing iron and sulphur. The further treatment of the solution exiting the first leaching stage comprises thickening and, after filtering, the removal of silver and mercury for instance. In the second stage, iron, arsenic, bismuth, mercury, antimony etc are removed by known methods. When the solution includes lead and zinc, the lead is recovered first with a separate electrolysis, and subsequently the zinc is recovered from the solution in another electrolysis. According to the publication, metal is produced on the cathode in both electrolyses, and the cathode is wiped so that both lead and zinc are removed in particulate form from the bottom of the cell.
The recovery of zinc and lead in electrolysis, in which particle-like metal is produced, is probably not in commercial use. There are difficulties in implementing it in practice in every case. The method also involves several halides in the solution entering electrolysis, which in the electrolyses form halide complexes such as BrCl.sub.2.sup.−. Although the formation of bromide complexes is advantageous from the point of view of raw material leaching, it causes considerable problems related to work hygiene.